WAN Technology Concepts

 Technology Overview

A variety of protocols and technologies are used in wide area networks. Some of these services, such as HDLC and Frame Relay, are explained in more detail later in coming blogs.

As described in relation to the OSI reference model, WAN  operations focus primarily on layer 1 and layer 2. WAN access standards typically describe both physical layer delivery methods and data link layer requirements, including physical addressing, flow control, and encapsulation. WAN access standards are define and managed by a number of recognized authorities, including the International Organization for Standardization (ISO), the Telecommunication Industry Association (TIA), and the Electronic Industries Alliance(EIA).

The data link layer (OSI Layer 2) protocols define how data is encapsulated for transmission toward a remote location and mechanism s for transferring the resulting frames. A variety of technologies are used, such as "Frame Relay" and "Asynchronous Transfer Mode"(ATM). Some of these protocols use the same basic framing mechanism , High-Level  Data Link Control (HDLC), an ISO standard, or one of its subsets or variants.

WAN Physical Layer Concepts

Includes several devices and terms specific to wide-area networks , as described in the following sections.

Terminologies 

One primary difference between a WAN and a LAN is that for a company or organization to use WAN  carrier network services , it must subscribe to an outside WAN service provider. A WAN uses data links provided by carrier services to access or connect the locations of an organizations to each other, to locations of other organizations, to external services, and to remote users. The WAN access physical layer describes

the physical connection between the company network and the service provider network.

1.) Customer Premises Equipment (CPE): The devices and inside wiring located at the premises of the subscriber, connected with a telecommunication channel of a carrier. The subscriber either owns or leases the CPE. A subscriber , in this context, is a company that arranges for WAN services from a service provider or carrier.

2.) Data Communications Equipment(DCE: Also called data circuit-terminating equipment, the DCE consist of devices that put data on local loop. The DCE primarily provides an interface to connect subscribers to a communication link on the WAN cloud .

3.) Local Loop: The copper or fiber cable that connects the CPE at the subscriber site to the central office(CO) of the service provider. The local loop is sometimes called the "last mile". 

4.) Demarcation point : A point established in a building or complex to separate customer equipment from service provider equipment. Physically, the demarcation point is the cabling junction box, located on the customer premises, that connects the CPE wiring to the local loop. It is usually placed for easy access by a technician. The demarcation point is the place where the responsibility for the connection changes from the user to service provider. This is very important, because when problems arise, it is necessary to determine whether the user or the service provider is responsible for troubleshooting or repair.

5.) Central Office(CO): A local service provider facility or building where local cables link to long-haul, all-digital, fiber-optic communication lines through a system of switches and other equipment.